Final answer:
Contour feathers on a bird are controlled by specialized muscles for movement and positioning, critical for creating a smooth aerodynamic surface during flight.
Step-by-step explanation:
Each contour feather on a bird is controlled by a set of specialized muscles and associated structures known as the musculature apparatus, which allows for the individual movement and positioning of these feathers. These structures ensure that the contour feathers create a smooth, aerodynamic surface, which is crucial for efficient flight by reducing the wind resistance, also known as form drag, against the bird's body.
Contour feathers differ from the bird's other types of feathers, such as flight feathers and down feathers. Flight feathers, including primary feathers and secondary feathers, are essential for generating lift and thrust, while down feathers are specialized for insulation.